Methods for designing and manufacturing transformers

ABSTRACT

Disclosed is an electrical transformer for improved transformer power capacity and efficiency designed by the application of disclosed design considerations. One embodiment design consideration is a method to configure power transformer windings wherein the minimum distance of the primary windings from the winding axis/core center is greater (the primary windings are more distal) from the winding axis than the minimum distance of the secondary windings, which are wound around the minimum interior core diameter. This design consideration is extended from single bobbin transformer designs to split bobbin designs, with the requisite distal increase of the primary windings (from the core axis) geometrically provided by an enlarged core bobbin center leg (axial) dimension beneath the primary winding window. Another disclosed design consideration is to fix the primary winding length relationship to the core weight for given transformer specifications in accordance with the disclosed unexpected experimental results and formula.

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application61/982,846 filed on Apr. 22, 2014. This application is a continuation ofand claims the benefit of U.S. non-provisional application Ser. No.14/522,195 filed on Oct. 22, 2014. Both applications are incorporatedherein in their entirety.

FIELD OF THE INVENTION

The field of the invention is electrical transformer design,specifically the optimization of transformer core and windingconfigurations for improved system power characteristics.

BACKGROUND

The natural link between electricity and magnetism may be explained inpart by a phenomenon known as magnetic flux. Electric current passingthrough an electrical conductor may induce magnetic flux in a proximatemagnetic material. This induced magnetic flux may then be carriedthrough a magnetic flux conductor to induce a second, electricallyinsulated current in an isolated proximate electrical conductor. Thislink between an electrically forced primary circuit, and a magnetic fluxcoupled but electrically insulated secondary electrical conductivecircuit has been well studied—including countless configurations of theelectrical conductors (windings) and the magnetic component (core).These properties of electromagnetism are used extensively to distributeenergy by electric transmission lines. Generated electric energy (at lowvoltages) may be converted efficiently by inductive transformers to veryhigh voltages which can be carried over long distances with minimalresistive heat losses, and then transformed similarly back to variousmuch lower useful voltages for operating our world of countlesselectrically driven devices.

Improvement in the electrical power transmission capacity and efficiencyby any fundamental variations of transformer winding (electricalconduction) or core configuration (magnetic flux), given the historicamount of study in this field would be a substantially unexpectedresult.

The long history of electricity transformer designs includesconsiderable efforts placed upon the configuration of the magnetic fluxcarrying segments of a transformer, also known as its core.

One of the oldest and most common configurations for transformers is anE-core transformer, which consists of many flat “E” shaped layers orlaminations of magnetic material electrically insulated from adjacentlayers to reduce eddy currents in the core. An insulated “I” shaped setof core laminations is the abutted to the “E” to form an “E-I” magneticcore.

Typical and well-known E core configuration transformers utilize thecenter leg of the E core to host both the primary and secondarywindings. Conventional transformer configurations are commonly designedwith the primary (high voltage) winding axially proximate to the corecenter axis, and the secondary (low voltage) winding wound on top of theprimary winding. Non-magnetic and electrically insulating “bobbins” aregenerally used for electrical safety and to facilitate manufacturing.The electrical windings are spun onto the bobbins, which are then slidor pushed onto the selected core segment. A common bobbin configurationwhich is known as a “split” bobbin, separates and insulates the primaryand secondary windings laterally from each other on the core center leg.Windings may consist of electrical wire wound around the core, orelectrically conductive thin ribbons wrapped around the core.

SUMMARY

Disclosed is an electrical power transformer design and design methodfor improved transformer power capacity and efficiency by theapplication of disclosed design considerations consistent with theinvention

A disclosed embodiment design consideration is a method for theoptimized selection of a primary winding length for a given set of modemcommercial transformer core lamination geometries.

Another embodiment design consideration is a method to configurestep-down power transformer windings wherein the minimum distance of theprimary windings from the winding axis/core center is greater (theprimary windings are more distal) from the winding axis than the minimumdistance of the secondary windings, which are wound around the minimuminterior core diameter.

This design consideration is extended from single segment or singlebobbin transformer designs to split bobbin designs, with theaforementioned distal increase of the primary windings (from the coreaxis) geometrically provided by an enlarged core center leg (axial)dimension beneath the primary winding window. This design considerationmay also be provided by a split bobbin with a greater axial spacingunderneath the primary winding.

Another disclosed design consideration is to fix the (optimal or ideal)primary winding length relationship to the core weight (within designproportions and of optimum permeability) in accordance with thedisclosed unexpected experimental results. For both disclosed designconsiderations, the secondary winding length is determined according tothe well-known corollary of Faraday's law which equates the ratio ofprimary and secondary winding length (generally expressed as a number ofwinding turns) and the primary and secondary voltage levels, or Np/NsVpVs, in order to meet output voltage requirements (the efficiencycorrelation parameter is omitted as it does not impact the ratiorelationship). The secondary winding gauge (thickness) is thendetermined to meet power requirements for the system. Unexpectedly, thisconfiguration reversal for the windings from a conventional design, suchthat when the primary winding length is held constant, the resultantcomponent modification creates additional space for the windings withinthe core window, which allows larger gauge windings to be used for thesame output voltage and thus provides greater power handling capacityfor the transformer.

The experimental results and experimentally derived results for anoptimized primary winding length matched to a given core weight aredisclosed for a given range, configuration and set of transformerspecifications. This relationship is identified analytically andextended illustratively to a defined range of potential transformerdesigns.

Such unexpected results and corresponding design considerations have inone embodiment been extended by a regressive natural logarithm curve fitto the experimental and experimentally derived data points disclosed. Abest-fit curve by a natural logarithm relationship was selected based onthe empirically illuminated process as asymptotic for these designfactors. This relationship is extended by disclosed factors for avariety of transformer specifications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A—Chart showing an optimized primary winding lengths for coreweights with the given specifications.

FIG. 1B—Empirically obtained and derived data points for optimal primarywinding lengths vs. core weight with corresponding curve fit naturallogarithm function.

FIG. 2A—Cross section/top view of lamination for E core type singlebobbin transformer showing winding configuration surrounding center legof the core.

FIG. 2B—Cross section/plan view of E core type single bobbin transformershowing winding configuration surrounding center leg of the transformercore.

FIG. 3—Cross section/top view of lamination for modified E core typesplit bobbin transformer showing primary and secondary windingconfigurations surrounding the modified split dimension center leg ofthe core.

FIG. 4A—Cross section/top view of core laminations for split bobbintransformers in typical prior art E-E type transformers.

FIG. 4B-4F—Cross section/top view of core laminations for split bobbintransformers with primary and secondary winding configurationssurrounding the modified split dimension center leg of the core. FIGS.4A-4D show modified E-E type transformer cores.

FIG. 4E shows a modified E-I type transformer core.

FIG. 4F shows a standard E-I type transformer core with a modified splitbobbin.

FIG. 5—Flow chart showing iterative design process for determiningoptimal winding length and wire gauge for power output.

DETAILED DESCRIPTION

Disclosed are several embodiments including various transformerconfigurations and design considerations which when followed result inimproved power capacity over the conventional design approaches fortransformers.

Conventional single bobbin transformer designs based on a E-Iconfiguration of core laminations are represented by a set oftransformer cores from Tempel Manufacturing, identified by Tempelcatalog part numbers as EI-X where X identifies the core geometryaccording to Tempel specifications. Based upon empirical and empiricallyderived results, the primary winding lengths for optimal powerefficiency in step-down configurations of transformers based upon thesecore lamination geometries was determined. As a generalized andunexpected result, the length of the primary winding was found to be thedriving factor for determining the optimal transformer configuration.Design considerations based upon this driving factor were thenconsidered and optimal configurations are disclosed. As discussed below,certain design considerations apply to both step-up and step-downconfigurations.

FIG. 1A is a chart of the optimal primary winding lengths determinedbased on core weights for the transformer with core characteristicsspecified herein. These values are graphed 101 in FIG. 1B with the coreweight (in pounds) shown on the x-axis 102, and the functionaloutput—the optimal primary winding length (in inches) is shown on they-axis 103. Exemplar data points are shown 104 106 which are connectedby a solid line. The determined data points are regressively curve fitto a natural logarithm function which reflects the asymptoticrelationship of the data. The determined curve fit for calculating theoptimal primary winding length in inches is shown 105 by a dashed lineand the equation y=−630*ln(x)+3360 identified as 107. Converted to feetof primary winding length, the relationship is y=−52.5*ln(x)+280. Unitsfor x is pounds (lbs) of core weight, and units for y is feet of primarywinding length.

For this embodiment, once the primary length is determined, thesecondary winding length may be determined according to the ratio ofinput and output voltages equivalency to input and output winding turns.As described below, for various embodiments when the primary winding islocated an increased axial distance from the core center, if the lengthof the primary remains constant, the number of turns around the coredecreases. Since the number of primary winding turns decreases for agiven configuration, the number of secondary winding turns must decreasein order to maintain the input to output ratio of turns (as specified bythe input and output voltages).

For this embodiment, the specified input voltage is 120 volts and thespecified output voltage is 24 volts. Core laminations for thisembodiment are specified as grade M 19 according to industry standardsfor the core material characteristics known as the AISI Grade—per theAmerican Iron and Steel Institute (AISI) Designation. The maximumtemperature (the target temperature after 2 hours of operation) for thisembodiment is 200° F., and the material for the windings is specified tobe copper. Input and output or primary and secondary voltages operate ata specified frequency, in these embodiments 60 Hz.

Other embodiments for determining the primary winding length may bereadily derived from the optimized relationship from Figure IA and IBaccording to several known and empirically derived relationship. Amongthese are that the primary winding length is directly proportional tothe primary winding voltage, and inversely proportional to the gauge ofthe primary winding. In one embodiment, the coefficient of the voltageto length relationship is 1, so for an input voltage of 240 volts ascompared to the specified input voltage of 120 volts, the primarywinding length is doubled. Also in this embodiment, the gauge of theprimary winding is reduced such that the cross sectional area (measuredin circular mils) is reduced by one-half.

In other embodiments in accordance with the optimized relationship fromFIGS. 1A and IB, the primary winding length is inversely proportional tothe industry standard allowable temperature. The coefficient for therelationship has a default of 1 with the value to be optimizedempirically. In other embodiments, the input idle current specified isinversely proportional to primary winding length. The coefficient forthe relationship has a default of 1 with the value to be optimizedempirically. In embodiments which utilize aluminum as the specifiedwinding material instead of copper, a significant power capacity lossmust be factored as a design consideration. In embodiments with aluminumwindings, the primary length is unchanged. In embodiments which utilizea core configured with magnetic material of various M grades accordingto AISI designation, the output power capacity may be increased ordecreased according to the core material, and according to embodimentswith alternate core materials, the primary winding length is unchanged;other transformer characteristics may be adjusted to meet powerrequirements for these embodiments.

Single bobbin transformer designs are commonly configured with theprimary and secondary windings wound around a single core segment. Forstep down transformers, the primary or high voltage winding is typicallywound closer to the core segment center axis, with the secondary, or lowvoltage winding wound outside the primary winding. By empirical andempirically derived analysis, the unexpected result of improved powercapacity was obtained for transformer configurations wherein the primarywinding (high voltage) is wound outside the secondary winding (lowvoltage). FIG. 2A shows a cross section 201 of the center leg 205 of anE geometry transformer core or otherwise configured single bobbintransformer. In this embodiment, the primary (high voltage) winding 204and secondary (low voltage) winding 203 cross-sectional areas arecomparable as is typical for conventional transformer designs. FIG. 2Bshows the same optimized single bobbin configuration 206 from the planview perspective, or looking end-on at the core segment 209 acting asthe windings bobbin. The primary (high voltage) windings 208 andsecondary (low voltage) windings 207 are shown configured according tothis embodiment, wherein the primary winding minimum axial distance fromthe core center 210 is greater than the secondary winding minimumwinding axial distance 211.

For the specific configuration of the embodiment shown in FIG. 2A, theprimary winding 19.5 gauge wire and 282 turns, with the secondarywinding 15.5 gauge wire with a total of 126 turns.

Locating the primary winding further from the core axial center of acomparable transformer configuration provides the unexpected utility ofincreased power capacity. For such embodiments when the primary windingis located at increased axial distance from the core center, if thelength of the primary winding remains constant, the number of turnsaround the core decreases. Since the number of primary winding turnsdecreases for a given configuration, the number of secondary windingturns must decrease in order to maintain the input to output ratio ofturns (as specified by the input and output voltages). When the numberof secondary windings is decreased, the length of the secondary windingconsequently decreases, and the amount of space occupied by the primaryand secondary windings in the core window decreases. The increasedavailable space for the windings in the window may then be utilized bylarger gauge windings, increasing the power capacity. This designconsideration is extended to other configurations for the transformer asdisclosed herein, but should not be construed to be limited to thesedisclosed embodiments as other will be apparent to those skilled in theart.

Split bobbin transformer designs are commonly configured with a coregeometry that isolates the primary and secondary windings onto adjacentbobbins surrounding the same core segment. In conventionally designedsplit bobbins with this configuration, the core center leg segment,which extends through both bobbins, has a given cross section dimension,diameter, or width. In an embodiment of the invention, split bobbintransformers with both bobbins surrounding the same core segment, thecore is configured with multiple such widths, which effectivelyincreases the primary winding minimum axial distance from the corecenter as compared to the secondary winding minimum winding axialdistance. FIG. 3 shows a cross-section view of a split-bobbinconfiguration consistent with this embodiment. Shown in FIG. 3, are theprimary (high voltage) bobbin 301 and secondary (low voltage) bobbin 302which are shown with the respective primary windings 303 and secondarywindings 304 in place. Also shown in FIG. 3 is an exemplaryconfiguration of the winding core 307 which positions the split bobbins301 and 302 with the chosen differential minimum axial winding distance305 and 306 for the primary and secondary windings from the core centeraxis 308. Also in accordance with this embodiment configuration, thesplit bobbin window widths 309 and 310, may be adjusted to compensatefor the change in window height such that the winding windows are ofcomparable cross-section areas.

For the specific configuration of the embodiment shown in FIG. 3, theprimary winding 19.5-gauge wire, wound at a width in the winding window28 winding turns across for a total of 306 turns. The secondary windingshown is 15.5-gauge wire with a winding window width of 11 windingsacross for a total of 126 turns.

Various core lamination configurations for split bobbins of E-E and E-Itype core geometries are shown in FIGS. 4A-4F. A typical core with anE-E geometry according to prior art is shown in FIG. 4A with the corelaminations creating the primary and secondary winding windows 401 and402. FIGS. 4B-4D show various E-E core lamination configurationsaccording to the split core or bobbin embodiment shown in FIG. 3. FIG.4E shows an E-I core lamination configuration according to the splitbobbin embodiment shown in FIG. 3. FIGS. 4B, 4C and 4D show E-Etransformer core laminations according to this embodiment, with thecenter legs 404, 406, 408 which hosts the primary windings 403, 405, 407having increasingly large widths, and abutting the center legs of the Elamination which hosts the secondary winding by configuring thelaminations with geometrically interlocking center leg segments 403,405, 407.

FIG. 4F shows an embodiment with a standard E-I core configuration 412with the center leg of the core 416 of a single width. In thisembodiment, a split bobbin 415 provides a winding surface whichseparates the primary winding 414 further from the core center leg 416than the secondary windings 413. Power capacity considerations may benecessary according to the magnetic properties of the core geometriesfor the embodiments in FIG. 4.

FIG. 5 presents an embodiment which details a generalized iterativeapproach for optimizing transformer core windings in accordance with thepresent invention. Once started 501, the user determines the initialspecifications or requirements for the desired step-down transformer502, including the input, primary or high voltage, the output,secondary, or low voltage, and the power requirements for thetransformer. Next 503, the secondary winding length Ls is estimatedaccording to the primary VP and secondary voltage Vs requirements andthe optimal primary winding length Lp according to the Faraday's lawcorollary such that Ls=Vs*Lp Np. Based upon the required power capacityof the transformer, the winding wire gauge (in mils) is determinedaccording to the empirically derived relationship of 4.5 W/mil forcopper and 7.37 W/mil for aluminum, for transformer output under load504.

Next the iterative process for experimentally optimizing the windinglengths is initiated winding the estimated secondary winding around thegiven core segment, and then winding the optimal primary winding lengtharound the secondary winding accordingly 505. Then output or secondaryvoltage is check against the specification requirements 506, and if notwithin specification, the secondary winding length is modified 507 andthe transformer is rewound and tested again 508. If the secondarywinding does not cover the winding window width 509, the gauge for thesecondary winding is increased 510 to cover the window width and thetransformer is rewound and retested 511. The last step for the iterativetesting is to check that the primary winding covers the availablewinding window 512 and if available space remains, the gauge for theprimary winding is increased 513, the transformer is rewound andretested. The process continues until the optimal winding lengths andwire gauges is determined 515.

Various alternative embodiments are available for the application ofaspects of the invention, including increasing the axial distance fromthe core center for the primary winding as compared with the secondarywinding for step-down (and step-up) transformers, including additionalsingle and split bobbin laminated core geometries, as well as toroidaltransformer cores.

The implications of the present invention's numerous potentialconfigurations and embodiments are far reaching. The unexpected findingof improved power capacity and efficiency for transformers designedaccording to the various embodiments of the invention allow transformersto operate at lower temperatures, save energy, or operate at the sameefficiency of existing conventional designs made with copper windingswith the use of aluminum windings, reducing both the cost of thetransformer and the weight.

Although the invention has been described in terms of the preferred andexemplary embodiments, one skilled in the art will recognize manyembodiments not mentioned here by the disclosed of the includedinvention embodiments and the included drawings. Interpretation shouldnot be limited to those specific embodiments disclosed in thisspecification.

The Commissioner is hereby authorized to charge any fees which may berequired with respect to this application to Deposit Account No. 505949.

We claim:
 1. A method for designing a transformer comprising: settingspecifications for the transformer input voltage, output voltage, andpower capacity, setting an initial primary winding length at a firstlength based on conventional transformer design criteria, estimating aninitial secondary winding length by calculating the secondary length Lto be the specified secondary voltage multiplied by said primary windinglength divided by the specified primary voltage, determining minimumwire gauges for the primary and secondary windings necessary to meetsaid specified power capacity wherein the initial winding lengths anddetermined initial wire gauges form the initial primary and the initialsecondary windings, winding the initial secondary winding around aselected secondary core segment, winding the initial primary windingaround a selected primary core segment, testing the output voltage ofthe transformer to determine whether the output voltage meets the outputvoltage specification, modifying iteratively the secondary windinglength and rewinding and retesting the output voltage until the outputvoltage meets the output voltage specification, testing the width ofwound secondary winding to determine whether the secondary windings fillthe selected secondary core segment, modifying iteratively the secondarywinding gauge and rewinding and retesting the secondary windings untilthe secondary windings fill the selected secondary core segment, testingthe width of wound primary winding to determine whether the primarywindings fill the selected primary core segment, modifying iterativelythe primary winding gauge and rewinding and retesting the primarywindings until the primary windings fill the selected primary coresegment.
 2. A method as in claim 1 wherein the selected primary coresegment and the selected secondary core segment are the center leg of astack of E shaped core laminations.
 3. A method as in claim 1 whereinthe selected primary core segment and the selected secondary coresegment are the center leg of a stack of E shaped core laminations,wherein said primary windings are wound on top of said secondarywindings.
 4. A method as in claim 1 wherein the selected primary coresegment is a center leg of a first stack of E shaped core laminationsand the selected secondary core segment is a center leg of a secondstack of E shaped core laminations which mirrors the orientation of thefirst stack of core laminations.
 5. A method as in claim 1 wherein theselected primary core segment is a center leg of a first stack of Eshaped core laminations and the selected secondary core segment is acenter leg of a second stack of E shaped core laminations which mirrorsthe orientation of the first stack of core laminations, and wherein thecenter leg of the first stack of core laminations is wider than thecenter leg of the second stack of core laminations.
 6. A method as inclaim 1 wherein the selected primary core segment is a first portion ofa center leg of a stack of E shaped core laminations and the selectedsecondary core segment is a second portion of the stack of E shaped corelaminations wherein the first portion of the center leg is wider thanthe second portion of the center leg.
 7. A method as in claim 1 whereinthe selected primary core segment and the selected secondary coresegment are the circumference of a toroidal magnetic core, wherein saidprimary windings are wound on top of said secondary windings.
 8. Amethod as in claim 1 wherein the transformer is a step-down transformer.9. A method as in claim 1 further comprising: adjusting the secondarywindings to compensate for a voltage loss.
 10. A method for designing atransformer comprising: setting initial primary and secondary voltagesand power capacity for the transformer, setting the weight and magneticpermeability of the transformer core, setting the conductive materialused for primary and secondary windings for the transformer, configuringa split bobbin for engaging the center leg of an E shaped magnetic corecomprising: a first section of said split bobbin with a first windingsurface, a second section of said split bobbin with a second sectionsurface, wherein said first section winding surface has a smallerdiameter than said second winding surface.
 11. A method for designing atransformer as in claim 10 further comprising: configuring the core ofthe transformer comprising a stack of magnetic core laminations of the Eshaped configuration, a center leg of said laminations comprising anenlarged portion to conform to the relatively large diameter windingsurface of said second section of the bobbin of claim
 9. 12. A methodfor designing a transformer as in claim 10, wherein the transformer is astep-down transformer.
 13. A method for manufacturing a transformercomprising: configuring a magnetic core of a specified magnetic materialdefining a geometry with a space for a primary and a secondary winding,setting an initial primary winding length at a first length based onconventional transformer design criteria, determining a length and gaugeof said secondary winding according to a ratio of said specified primaryvoltage and said specified secondary voltage multiplied by a number ofturns determined by the length of said primary winding length andoptimized to utilize said space, winding said secondary winding about abobbin which engages said core, winding said primary winding about saidbobbin outside of said secondary winding, affixing said bobbin to aselected segment of said core.
 14. A method for manufacturing atransformer as in claim 13, wherein said winding of said secondarywinding and the winding of said primary winding is about a split bobbinwhich laterally spaces the primary and secondary windings, wherein saidprimary winding minimal axial distance from an axial center of saidselected core segment is greater than said secondary winding minimalaxial distance from said axial center of said selected core segment. 15.A method as in claim 13 further comprising: adjusting the secondarywindings to compensate for a voltage loss.
 16. A method formanufacturing a transformer as in claim 13, wherein the transformer is astep-down transformer.